The present invention relates to disposable absorbent articles. Disposable absorbent articles are considered to be absorbent devices designed to be worn externally of the body by a user and to receive fluids discharged from the body. In particular the present invention relates to disposable absorbent pantiliners, sanitary napkins, catamenials, and incontinence inserts, that are anatomically shaped and exhibit an increased ability to recover their original substantially flat configuration after folding.
In their basic form, disposable absorbent articles comprise an absorbent core interposed between a pervious body-contacting element (alternatively referred to as a topsheet or an overwrap) and an impervious protective barrier (alternatively referred to as a backsheet). The absorbent element is, of course, intended to receive and contain the fluids discharged from the body. The body-contacting element is intended to provide comfortable and dry-feeling contact with body surfaces while allowing free passage of fluids therethrough into the absorbent element. The protective barrier is intended to prevent the fluids which are expelled or which escape from the absorbent element from soiling the user""s garments.
Disposable absorbent articles are usually intended to be applied to the panty, and typically fixed to it by an adhesive, before wearing the panty with the applied absorbent article. The shape of disposable absorbent articles, as seen in plan view, has developed from a traditional, substantially rectangular shape to anatomical shapes having widths that are not constant along the length of the article and that are intended to cover additional body area as compared to a traditional rectangular product having a width corresponding to the minimum width of a shaped article. Anatomically shaped articles provide a better comfort for the user owing to their shape that better conforms to the user""s anatomy, and that at the same time more closely follow the shape and contours of the panty in the crotch region, where the articles are applied, so ensuring an increased protection for the garment.
Most common anatomical shapes for disposable absorbent articles are those in which the article has a minimum width in its central portion, and is larger in its front and/or in its rear portion. The portions of the article that extend laterally in the front and/or in the rear end portion beyond this minimum width allow the absorbent article longitudinal edges to better match the contour of the panty in the crotch zone.
Such anatomically shaped disposable absorbent articles usually have an absorbent core with rectilinear, parallel longitudinal edges. The topsheet and the backsheet extend beyond the absorbent core in the portions of the absorbent article that are wider than the minimum width, and here they form lobes or ears of the article.
Disposable absorbent articles are typically applied to the user""s garment in a substantially flat configuration, by xe2x80x9csubstantially flatxe2x80x9d being meant substantially void of folds or wrinkles. During the use the article deforms and bends under the forces exerted by the user""s body and by the garment, and a certain degree of deformation is indeed accepted and preferred, since it causes the absorbent article to conform to the wearer""s body, therefore providing a better comfort and protection.
A disadvantage that has been experienced with anatomically shaped disposable absorbent articles comprising lobes or ears is due to the possible folding of the lobes during the use, which can cause the formation of permanent folds, generally resulting in a reduction of the useful surface of the article itself. The amount of the folding can range from few degrees, relative to the initial, substantially flat configuration, to the complete folding of a portion of a lobe, or also of the entire lobe, over or down the product. Various types of folds are possible, such as for example C-, Z-, S-, or W-shaped folds. Occurrence of such folding in the lobes of anatomically shaped absorbent articles can in fact be promoted by the longitudinal edges of the absorbent core in that they could constitute a sort of line of preferential folding for the lobes, since the article has, along these edges, a change in thickness and therefore in stiffness and resiliency. Moreover, the low overall thickness of the article can make it easier a complete folding of the lobes over or under the article itself.
This problem is less evident in traditional anatomically shaped disposable absorbent articles, where the intrinsic resiliency of the materials constituting the lobes can avoid, at least to a certain extent, the formation of permanent folds, even after a certain degree of folding has taken place, e.g. by helping the unfolding of the folded portions.
However, the problem of the formation of permanent folds in the lobes has become more evident in anatomically shaped disposable absorbent articles provided with improved backsheets comprising at least two layers laminated or otherwise joined together to make a unitary structure having specific properties.
Multilayer backsheets that are particularly preferred in disposable absorbent articles are those providing breathability.
The provision of breathable products has been considered a means for providing consumer comfort benefits in absorbent articles. Breathability has typically concentrated on the incorporation of so called xe2x80x9cbreathable backsheetsxe2x80x9d in the absorbent articles. Breathable backsheets are water vapour permeable, preferably air permeable, allowing gaseous exchange with the environment. This thereby allows for the evaporation of a portion of the fluid stored in the core and increases the circulation of air within the absorbent article. The latter is particularly beneficial as it reduces the sticky feeling experienced by many wearers during use, commonly associated with the presence of an apertured formed film or film like topsheet, particularly over extended periods of time. This is a result of topsheets designed to achieve a clean and dry appearance. These topsheets tend to be smooth thereby minimising the build up of fluid on the surface of the topsheet. However, these benefits are achieved at the expense of comfort, particularly under hot and humid conditions, when due to their smooth surface texture they tend to become sticky to the skin.
However, the main drawback associated with the use of breathable backsheets in absorbent articles is the negative effect on the protection level performance, by leakage known as wet through onto the users garment. Although, breathable backsheets in principle only allow the transfer of materials in the gaseous state, physical mechanisms such as extrusion, diffusion and capillary action may still occur and result in the transfer of the fluids from the absorbent core through the backsheet and onto the users garments. In particular, these mechanisms become more dominant if the product is utilised during physical exertion, or for heavy discharge loads or over extended periods of time. Thus, whilst the incorporation of breathable backsheets in absorbent articles is highly desirable from a comfort standpoint, since the primary role of a backsheet still remains the prevention of liquid leakage, it is necessary that such breathable backsheets are also fluid impervious in order to avoid the risk of wet through.
Dual layer breathable backsheets as those described e.g. in International Patent Applications WO 96/14037, WO 97/24095, WO 97/24096 and in European Patent Application EP 96830343.8 are particularly effective in providing both breathability and fluid imperviousness against the risk of wet through. They are particularly suitable for incorporation in thin products such as pantiliners or thin sanitary napkins. Preferred structures for such dual layer breathable backsheets usually comprise a gas permeable apertured tridimensional polymeric film, typically as the inner layer, i.e. closer to the absorbent core, adhered or in any case associated to an outer layer constituted by a gas permeable fibrous fabric layer, or, alternatively, by a gas permeable microporous polymeric layer.
Such dual layer backsheets have shown a very good behaviour in terms of breathability and wet through control, and constitute a structure that is still thin and flexible but, owing to its relative complexity, is less resilient and may increase the possibility of the formation of permanent folds in the lobes in anatomically shaped breathable products during the use. The tridimensional structure of the apertured tridimensional polymeric film for example can crush during folding and this may induce the formation of permanent or quasi permanent folds in the lobes of the shaped sanitary article during the use.
Disadvantages of the lobe folding with formation of permanent folds in the anatomically shaped disposable absorbent articles are mainly due to the decrease in the product absorbing and protecting performance caused by the reduction of the effectively useful surface area of the product, and also to the negative perception of the product quality and performance by the user when she becomes aware, usually at the time she removes the article from the garment, that the article itself has lost, to a certain extent, its initial optimal configuration. Folded lobes can moreover induce a comfort issue for the user during use of the article, since they constitute zones where the article is thicker and possibly stiffer.
It is therefore an object of the present invention to provide an anatomically shaped disposable absorbent article having a reduced tendency to form permanent folds in the lobes during the use, i.e., having a better ability to recover the initial unfolded configuration after folding.
It is a further object of the present invention to provide such an article with a reduced tendency to form permanent folds in the lobes, which is moreover breathable.
It has in fact been discovered that by controlling the joining between the superimposed layers that constitute the shaped disposable absorbent article in the lobe area it is possible to reduce the tendency of the shaped article to form permanent folds in the lobes during the use.
The present invention refers to a shaped disposable absorbent article having a front end portion and a rear end portion, and a periphery. The shaped disposable absorbent article is constituted by superimposed layers comprising a liquid pervious topsheet, a backsheet comprising at least two layers, and being joined to said topsheet at least along the periphery, and an absorbent core intermediate the topsheet and the backsheet, and has at least one lobe in at least one of the front end portion or rear end portion, the lobe being provided inside the periphery by the topsheet and the backsheet in a region where the topsheet and the backsheet extend beyond the absorbent core. The shaped disposable absorbent article has a joining ratio in the at least one lobe defined as the ratio having as the numerator the number of superimposed layers being directly joined to at least an adjacent layer in the at least one lobe other than along the periphery, and as the denominator the total number of the superimposed layers in the at least one lobe. The joining ratio has a value that is lower than or equal to 0.5.